1. Field of the Invention
This invention pertains generally to rotary dynamoelectric machines, and more particularly to dynamoelectric machines having novel rotor and stator structures, to generators having permanent-magnet axial-field rotor and stator disks, and further to cooperative integrated electronics for wide range power control and efficient electric power interface with loads.
Applicant sets forth a brushless self-synchronous generator with permanent-magnet rotor disks and stator winding disks, including integral electronics, to efficiently generate DC (direct-current) electric power, at current and voltage regulated by the electronics, from broadly variable speed rotary mechanical drive. Its various embodiments are intended to generate useful electric power efficiently, especially at low speed and torque, from a wide variety of variable speed and torque drive sources. Moreover, it is intended to substantially improve and expand sustainable environmentally responsible energy options, such as wind power, hydrodynamic power, and human-power-assisted electric vehicles. A main embodiment is intended to generate better quality electric power from wind turbines, and higher energy yields, compared to prior art wind turbine generators.
2. Description of the Related Art
Poly-phase (usually 3-phase) alternating-current (AC) salient-pole induction machines, having wound stators and rotors, are presently directly connected to power grids in “wind farms” to augment grid power from windy locations. They do not incur major grid synchronization problems, as do directly connected synchronous generators, which are mostly used in generating plants where their shaft speed is regulated and output carefully synchronized prior to parallel connection with on-line generators. However, induction machines generate power only when shaft speed exceeds that needed at zero slip speed. They cannot self-start from turbine drive, and consume grid power (not augment it) whenever their speed falls below a critical zero slip speed level. Moreover, their power is unregulated, and they must be disconnected from the grid at very high wind speeds, because their power fluctuations and internal generator heating are excessive. For a comprehensive analysis and Thevenin equivalent circuits of induction machines, see, for example, the textbook “Electric Machinery” (an integrated treatment of AC and DC machines) McGraw-Hill Book Co. 1952, by Fitzgerald & Kingsley, Massachusetts Institute of Technology, Chapter 3 (especially page 131 and Chapter 9). For further analysis and performance prediction of broader speed range but less efficient 2-phase induction machines, see “Effects of Phase-Shift and Distortion on Servomotor Performance,” 1960, by Richard B. Fradella, MSEE research and thesis, California Institute of Technology.
Peripheral equipment needed for augmenting grid power from wind turbines, which drive induction generators, may include gears to increase generator shaft speed, switchgear to connect and disconnect said generators from the grid as wind speed varies, gear lubricant, pumps and heat exchangers to cool the lubricant, a generator cooling system, and external heat-dumps.
Over the past two decades, power electronics has been developed to provide a power control interface between induction machines and DC voltage supplies such as chemical batteries. This electronics converts the DC voltage to substantially variable-frequency poly-phase voltage (albeit with high distortion) at the induction machine poly-phase terminals, enabling these machines to perform as bi-directional motors or generators. For example, an induction machine with applied fundamental frequency component appropriately higher than its electrical frequency at a given shaft speed can be driven as a variable-speed induction motor, from zero to a desired speed. With its shaft driven by rotary power, the same induction machine with applied poly-phase voltage having a frequency appropriately lower than its electrical frequency at a given shaft speed can instead generate power as a variable-speed induction generator. By reversing the poly-phase sequence, the induction machine can likewise drive in the opposite direction, or can generate power from a shaft driven in the opposite direction. Silicon Controlled Rectifier (SCR) power switching semiconductors are useful as the DC to poly-phase power switching interface for induction machines, because they are rugged and can control considerably higher power than comparable cost high-frequency switching semiconductors. Moreover, the iron cores of said induction machines have high inductance, so it is not feasible to use a series low-loss ferrite core inductor as described for the present invention. Induction machine core loss would be very high, with attendant heating problems, if subjected to high-frequency switching pulse-duration-modulation (PWM) to provide poly-phase sinusoidal voltages having low harmonic distortion across the induction machine stator winding terminals.
Prior art inventions that provide examples of power interface electronics for variable-speed induction machines that are driven by chemical batteries and regenerate power thereto include: U.S. Pat. No. 5,099,186 by Rippel et al; and U.S. Pat. No. 5,355,070 by Cocconi.
Synchronous AC generators include salient-pole alternators having wound stators and permanent-magnet rotors. Their output voltage and frequency are substantially proportional to their shaft speed. Brushless salient-pole reluctance machines having wound stator poles with magnetic bias from permanent magnets, is one type. Those generators may include field windings, to afford limited voltage regulation. Homopolar machines are also a synchronous brushless type, with their power output frequency proportional to speed; they afford wider range voltage adjustment. If their field is derived only from a field winding, they will need electric startup power for that winding. Cogging torque (wherein the rotor angle aligns its iron cores with and holds minimum magnetic reluctance positions), like stiction and friction in gears, may cause wind turbines to stall at low wind speeds. These shortcomings and too low output voltage at low shaft speeds prevent usable power generation at low wind speeds from this prior art machine. Adding a boost regulator in series with the rectified and filtered alternator type generator output can facilitate higher voltages at low shaft speeds, needed for loads such as chemical batteries, but the boost regulator incurs tandem losses and machine cogging may stall the wind turbine driving it so no electric power output is produced from this prior art machine at low wind speeds.
By comparison, the present invention is intended to generate power at requisite voltage over its entire wide speed range, will not need electric startup power from its load or any other external source, and will efficiently generate power even from very low shaft torque rotation from low wind speeds, not stalled by cogging torque, stiction, or friction.
Besides their use for AC power generation in power plants, applications for synchronous generators range widely, usually with their AC outputs rectified, to charge batteries and the like. However, their varying voltage and frequency can be a major disadvantage. Generated and rectified voltage must be sufficient, and usually regulated, to meet needs of given applications. Moreover, very low frequency ripple at low shaft speed requires large filter capacitors, which cost more and have shorter lifetimes than ceramic or film capacitors. These properties usually limit synchronous generator applications to high shaft speeds. Their cogging torque is another drawback. Peripheral equipment needed for augmenting grid power, from alternators used as generators driven by wind turbines, usually include gears to increase generator shaft speed, rectifiers to convert their AC outputs to DC, and power inverters to convert the DC to regulated AC in phase with the grid. Moreover, their varying output voltage and current must be regulated, for chemical battery charging applications; which requires a battery charger.
Brush-commutated DC generators may have permanent-magnet field excitation. They may also have field excitation windings, for limited output voltage adjustment. Besides shorter lifetimes due to their commutator brush and armature wear, commutator sparking can be troublesome; and, similar to most prior art generators, their DC output voltage is proportional to speed, thus precluding many low shaft speed applications, unless their output is connected to loads via boost regulator circuits. Alternatively, their varying output voltage and current may require a buck regulator, between the generator output and its load. Such external and series electronics reduces overall power efficiency, particularly at low turbine shaft speeds.
Regardless of said drawbacks, these machines are widely used as generators for some applications. Peripheral equipment, for use as generators driven by wind turbines, may include speed-up gearing and output rectifiers. Said rectifiers may be needed, to prevent power from a DC power-bus load, which it feeds, such as chemical batteries it is meant to charge, from driving said DC generator as a motor, and discharging connected batteries whenever the generator output voltage is less than the battery voltage. Power regulator circuits, such as battery chargers, are usually needed. Besides these limitations, brush-commutated generators also need periodic commutator maintenance; as their commutators are damaged with use, by wear and sparking.
Gearing needed to increase prior art generator shaft speed, so prevalent in wind power systems, also needs bearings for the gears, is subject to wear, needs periodic maintenance, and incurs power losses. The gearing stiction further inhibits and usually prevents power generation at low wind speeds. Conversely, the present invention, having no cogging torque and no speed-up gearing, is intended to generate power over a very wide speed range.
Most electric motors can be used as generators. There is fundamentally no difference, between most prior art motors and generators, of a specific type, except for how they are used to meet needs of specific applications. For example, an induction machine can serve as an induction motor or as a generator. Motors used in ubiquitous machinery, tools, and appliances can be configured mechanically and electrically as generators.
Insofar as drive speed and torque is regulated at steam driven and large hydroelectric power plants, the prior art generators described above have provided acceptable options, to generate most of the electric power that is distributed by power grids, for over a century.
Smaller and portable versions of said generators, driven by fuel-burning engines, also serve viable small markets. However, need for wider speed range has been long recognized.
Some prior art inventions have intended to accommodate variable-speed drives, by means substantially different from my present invention:
U.S. Pat. No. 4,694,187 “Electromechanical Constant Speed Drive Generating System” by Baker, includes a mechanical differential gear, to obtain constant speed drive for a generator. It is mainly intended to accommodate variable-speed aircraft engine drive, by including controlled variable compensatory drive. It does not teach a generator assembly similar to the present invention, nor does it include electronics similar to the present invention.
U.S. Pat. No. 6,969,922 “Transformerless Load Adaptive Speed Controller” by Welches, includes electromechanical means, to obtain constant speed generator drive, from a variable-speed drive source. Its generator assembly is substantially different from the present invention, and it does not teach electronics similar to the present invention.
U.S. Pat. No. 5,982,074 “Axial Field Motor/Generator” by Smith et al and my U.S. Pat. No. 4,530,200 teach, with some differences, a motor/generator assembly having multi-pole axial magnetic field rotor disks and stator disks between them, but they do not set forth electronics similar to the present invention, intended to efficiently generate regulated electric power over a broad speed range.
U.S. Pat. No. 5,245,238 “Axial Gap Dual Permanent Magnet Generator” by Lynch et al, describes means for generating constant output voltage that do not include electronics similar to the present invention. Its generator assembly and rotor disks are also distinctly different from those herein described in all embodiments of the present invention.
U.S. Pat. No. 7,190,101 “Stator Coil Arrangement for an Axial Airgap Electric Device Including Low-Loss Materials” by Hirzel, teaches a substantially different generator assembly and materials, and does not set forth electronics similar to the present invention.
U.S. Pat. No. 5,021,698 “Axial Field Electrical Generator” by Pullen et al, describes a high-speed generator assembly substantially different from the present invention, and does not describe electronics.
U.S. Pat. No. 6,217,398 “Human-Powered Or Human-Assisted Energy Generation And Transmission System With Energy Storage Means And Improved Efficiency” by Davis; and U.S. Pat. No. 7,021,978 “Human-Powered Generator System With Active Inertia And Simulated Vehicle” by Jansen; describe means to use variable effort pedal power. They teach using electric generators with operator adjustable control means, and their advantages over mechanical drives, for augmenting vehicle power, in applications including electric vehicles, watercraft, and the like. However, they do not teach generator assembly configurations nor an electronics power interface as set forth in the present invention.
Other exemplary patents for rotary dynamoelectric machines and for other apparatus which may or may not be related but which provide illustration from which the teachings are incorporated herein by reference, include: U.S. Pat. No. 295,534 by Frick; U.S. Pat. No. 459,610 by Desroziers; U.S. Pat. No. 1,566,693 by Pletscher; U.S. Pat. No. 2,743,375 by Parker; U.S. Pat. No. 2,864,964 by William Kober; U.S. Pat. No. 3,050,650 by Jacques; U.S. Pat. No. 3,069,577 by Royal; U.S. Pat. No. 3,090,880 by Henri; U.S. Pat. No. 3,091,711 by Jacques; U.S. Pat. No. 3,124,396 by Barager; U.S. Pat. No. 3,219,861 by Burr; U.S. Pat. No. 3,230,406 by Jacques; U.S. Pat. No. 3,231,807 by Willis; U.S. Pat. No. 3,239,702 by Van De Graaff; U.S. Pat. No. 3,304,598 by Jacques; U.S. Pat. No. 3,337,122 by Johann; U.S. Pat. No. 3,375,386 by Hayner et al; U.S. Pat. No. 3,401,284 by Park; U.S. Pat. No. 3,407,320 by Mclean; U.S. Pat. No. 3,441,761 by Painton et al; U.S. Pat. No. 3,569,753 by Babikyan; U.S. Pat. No. 3,584,276 by Ringland et al; U.S. Pat. No. 3,696,277 by Liska et al; U.S. Pat. No. 3,731,984 by Habermann; U.S. Pat. No. 3,796,039 by Lucien; U.S. Pat. No. 3,845,339 by Heinzmann et al; U.S. Pat. No. 3,899,731 by Smith; U.S. Pat. No. 3,982,170 by Gritter et al; U.S. Pat. No. 4,127,799 by Nakamura et al; U.S. Pat. No. 4,207,510 by Woodbury; U.S. Pat. No. 4,228,391 by Owen; U.S. Pat. No. 4,264,856 by Frierdich et al; U.S. Pat. No. 4,295,083 by Leenhouts; U.S. Pat. No. 4,358,723 by Scholl et al; U.S. Pat. No. 4,371,801 by Richter; U.S. Pat. No. 4,384,321 by Rippel; U.S. Pat. No. 4,390,865 by Lauro; U.S. Pat. No. 4,394,597 by Mas; U.S. Pat. No. 4,415,963 by Rippel et al; U.S. Pat. No. 4,417,194 by Curtiss et al; U.S. Pat. No. 4,426,613 by Mizuno et al; U.S. Pat. No. 4,483,570 by Inoue; U.S. Pat. No. 4,513,214 by Dieringer; U.S. Pat. No. 4,618,806 by Grouse; U.S. Pat. No. 4,645,961 by Malsky; U.S. Pat. No. 4,656,413 by Bourbeau; U.S. Pat. No. 4,694,187 by Baker; U.S. Pat. No. 4,734,839 by Barthold; U.S. Pat. No. 5,021,698 by Pullen et al; U.S. Pat. No. 5,117,141 by Hawsey et al; U.S. Pat. No. 5,204,569 by Hino et al; U.S. Pat. No. 5,258,697 by Ford et al; U.S. Pat. No. 5,289,361 by Vinciarelli; U.S. Pat. No. 5,341,075 by Cocconi; U.S. Pat. No. 5,392,176 by Anderson; U.S. Pat. No. 5,419,212 by Smith; U.S. Pat. No. 5,441,222 by Rosen; U.S. Pat. No. 5,495,221 by Post; U.S. Pat. No. 5,514,923 by Gossler et al; U.S. Pat. No. 5,525,894 by Heller; U.S. Pat. No. 5,614,777 by Bitterly et al; U.S. Pat. No. 5,681,012 by Rosmann et al; U.S. Pat. No. 5,705,902 by Merritt et al; U.S. Pat. No. 5,712,549 by Engel; U.S. Pat. No. 5,717,303 by Engel; U.S. Pat. No. 5,729,118 by Yanagisawa et al; U.S. Pat. No. 5,754,425 by Murakami; U.S. Pat. No. 5,783,885 by Post; U.S. Pat. No. 5,798,591 by Lillington et al; U.S. Pat. No. 5,847,480 by Post; U.S. Pat. No. 5,861,690 by Post; U.S. Pat. No. 5,880,544 by Ikeda et al; U.S. Pat. No. 5,883,499 by Post; U.S. Pat. No. 5,969,446 by Eisenhaure et al; U.S. Pat. No. 5,977,677 by Henry et al; U.S. Pat. No. 5,977,684 by Lin; U.S. Pat. No. 6,011,337 and U.S. Pat. No. 6,049,149 by Lin et al; U.S. Pat. No. 6,121,704 by Fukuyama et al; U.S. Pat. No. 6,130,831 by Matsunaga; U.S. Pat. No. 6,137,187 by Mikhail et al; U.S. Pat. No. 6,166,472 by Pinkerton et al; U.S. Pat. No. 6,246,146 by Schiller; U.S. Pat. No. 6,259,233 by Caamano; U.S. Pat. No. 6,262,505 by Hockney et al; U.S. Pat. No. 6,288,670 by Villani et al; U.S. Pat. No. 6,388,347 by Blake et al; U.S. Pat. No. 6,407,466 by Caamano; U.S. Pat. No. 6,750,588 by Gabrys; U.S. Pat. No. 6,815,934 by Colley; U.S. Pat. No. 6,858,962 by Post; U.S. published patent application 2006/0208606 by Hirzel.
Additional patents by the present inventor, the teachings which are additionally incorporated herein by reference, include: U.S. Pat. Nos. 4,085,355 and 4,520,300 by Fradella; U.S. Pat. Nos. 6,566,775 and 6,794,777 by Fradella.